Engines may include crankcase ventilation systems to vent gases out of the crankcase and into an engine intake manifold to provide continual evacuation of gases from inside the crankcase in order to reduce degradation of various engine components in the crankcase. The crankcase ventilation system may include a positive crankcase ventilation valve (PCV valve) for enabling one-way flow of crankcase gases from inside the crankcase to the intake manifold.
Crankcase ventilation systems may be intermittently diagnosed for PCV valve degradation. One example approach for PCV valve diagnostics is shown by Satou in US 2009/0211545. Therein, PCV valve degradation is determined based on air changes (e.g., changes to a throttle position) and fuel changes (e.g., fuel injection adjustments) required to maintain an idle speed as an opening of the PCV valve is adjusted. The opening of the PCV valve is, in turn, selected based on an air/fuel ratio of blow-by gas.
However, the inventors herein have recognized potential issues with such approaches. As one example, the blow-by based diagnostics approach may have significant noise issue due to various engine loads. These include, for example, engine friction, barometric pressure, AC compressor load, alternator load, etc. Consequently, computation intensive noise reduction algorithms may be required.
In one approach, to at least partially address these issues, a method for an engine crankcase ventilation system is provided. The method comprises, indicating degradation of a valve coupled between a crankcase and an intake manifold based on characteristics of a transient drip in crankcase vent tube pressure during engine cranking. In this way, existing hardware can be used to diagnose PCV valve degradation.
In one example, an engine crankcase ventilation system may include a crankcase vent tube coupled between an air intake passage and a crankcase. A pressure sensor (or flow sensor) may be positioned within the crankcase vent tube for providing an estimate of flow or pressure of air flowing through the vent tube. During engine cranking, an estimated crankcase vent tube pressure profile may be compared to an expected crankcase vent tube pressure profile. In particular, during engine cranking and run-up when manifold vacuum is low, if the PCV valve is working properly, a flow rate through the crankcase vent tube may be expected to increase since the engine speed is increased through crank and run up and the PCV valve is initially in the lowest restriction position. When the manifold vacuum reaches a threshold, the flow rate through the vent tube may be expected to decrease and stabilize. This may be reflected as a transient dip in crankcase vent tube pressure during engine cranking. Thus, based on the estimated crankcase vent tube pressure profile not matching the expected crankcase vent tube pressure profile, a controller may determine that the PCV is degraded. For example, based on an amplitude of the transient dip in crankcase vent tube pressure being smaller that the expected amplitude (or a threshold value), it may be determined that the PCV valve is stuck closed (or in a low flow position). As another example, based on the amplitude of the transient dip in crankcase vent tube pressure being higher that the expected amplitude (or threshold value), it may be determined that the PCV valve is stuck open (or in a high flow position).
In this way, by correlating changes in crankcase vent tube pressure with changes in crankcase vent air flow and PCV valve position, PCV valve degradation can be reliably detected. By using an existing crankcase ventilation system pressure sensor to identify PCV valve degradation, the need for additional sensors as well as computation intensive noise reduction algorithms is reduced, providing cost and complexity reduction benefits, without reducing an accuracy of degradation detection. Further, the approach enables the crankcase ventilation system to remain active during a diagnostic procedure.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.